At the start of summer, hundreds of elephant carcasses were spread across Botswana’s Okavango Delta. For months, what killed the more than 300 elephants between late April and June was a mystery, with many wondering if poachers were somehow involved or if something sinister might be at play. Now, officials say the pachyderms were laid low by toxic blue-green algae that had polluted their drinking water, reports BBC News.
Botswana is home to the world’s largest population of elephants—roughly 130,000 and rising—making the country a premier destination for wildlife tourism, report Mqondisi Dube and Max Bearak for the Washington Post.
The blooms of blue-green algae, which is actually not a true algae but a type of cyanobacteria, took hold in seasonal pools of water used by elephants, says Cyril Taolo, Botswana’s acting director of the Department of Wildlife and National Parks. The deaths came to a halt once these ephemeral ponds dried up, reports Sello Motseta of the Associated Press.
Elephants of all ages and both sexes were found dead, with most of the bodies discovered near watering holes.
Tensions between elephants and people have increased in parts of Botswana, where the massive mammals are often blamed for destroying crops, per the Post. A promise to do more to keep elephants under control featured in the successful re-election campaign of President Mokgweetsi Masisi, and his administration has reintroduced a small number of elephant hunting licenses.
In the statement, Taolo says, “there is absolutely no reason to believe there was human involvement in these mortalities.” Poachers are considered unlikely culprits because the dead elephants retained their ivory tusks, which fetch top dollar on the black market.
No other species of wildlife appear to have been impacted by the toxic algal blooms. Even scavengers, such as vultures and hyenas, seen feeding on the glut of colossal corpses showed no apparent ill effects, according to the AP. Taolo offered no explanation for why only elephants were affected, which, the Post notes, may complicate the narrative that human involvement can be ruled out.
Keith Lindsay, a biologist who has studied elephants for 40 years and who served in Botswana’s wildlife ministry under Massi’s predecessor, tells the Post that despite the announcement of the results of the government’s analysis, he thinks that the elephants in the Okavango were “targeted.” He suggests the tests performed by the wildlife ministry failed to rule out neurotoxins that may be available to farmers and thus did not rule out foul play. Lindsay is calling on the government to release the full test results to the public.
Map Ives, who has worked on elephant conservation projects in Botswana for decades, tells the Post that toxic cyanobacteria seems like a probable explanation for the deaths. He adds that in the Okavango Delta, water levels have been rising in recent years, which may have carried cyanobacteria present deeper in the soil up to the surface.
In sufficiently high doses, cyanobacteria can kill mammals by interfering with the nervous system’s ability to send signals throughout the body. This can eventually cause paralysis and cardiac or respiratory failure. Many of the elephants that died in Botswana were seen walking in circles before dying suddenly, some collapsing onto their faces, reports Phoebe Weston for the Guardian.
In a statement quoted by the AP, Taolo says “a monitoring plan of seasonal water-pans on a regular basis to track such future occurrences will be instituted immediately and will also include capacity building to monitor and test for toxins produced ... by cyanobacteria.”